Electrical, high temperature test probe with conductive driven guard

ABSTRACT

A probe needle apparatus having a conductive central core with alternating layers of dielectric and conductive materials is provided. The apparatus includes the conductive central core, a first layer of dielectric material applied to maintain electrical access to the conductive central core while providing continuous isolation of the conductive central core elsewhere, and a conductive driven guard layer applied around the first layer of dielectric material in electrical isolation from the conductive central core. The conductive driven guard layer is applied on the first layer of dielectric material with a mask on an end of the conductive central core to prevent the conductive driven guard layer from touching the conductive central core.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority to U.S. Provisional PatentApplication Ser. No. 60/458,467, filed on Mar. 28, 2003, and is relatedto U.S. patent application Ser. No. 09/730,130, filed Dec. 4, 2000, nowU.S. Pat. No. 6,586,954, entitled “PROBE TILE FOR PROBING SEMICONDUCTORWAFER”; U.S. Provisional Patent Application Ser. No. 60/392,394, filedJun. 28, 2002, entitled “SHIELDED PROBE APPARATUS FOR PROBINGSEMICONDUCTOR WAFER”; and U.S. patent application Ser. No. 10/383,079,filed Mar. 6, 2003, entitled “APPARATUS AND METHOD FOR TERMINATING PROBEAPPARATUS OF SEMICONDUCTOR WAFER”; the subject matter of which areincorporated herewith by reference.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor test equipment,and more particularly, to a probe apparatus used in semiconductor testequipment for electrically probing devices on a semiconductor wafer.

BACKGROUND OF THE INVENTION

The semiconductor industry has a need to access many electronic deviceson a semiconductor wafer. As the semiconductor industry grows anddevices become more complex, many electrical devices, most commonlysemiconductor devices, must be electrically tested, for example, forleakage currents and extremely low operating currents. These currentsare often below 100 fA. In addition, the currents and devicecharacteristics are often required to be evaluated over a widetemperature range to understand how temperature affects a device. Also,because of materials characteristics of dielectrics, it is oftendifficult to test characteristics of semiconductor devices in a wideoperating temperature range.

To effectively measure at currents below 100 fA (Femto Ampere), ameasurement signal must be isolated from external electricalinterference, leakage currents through the dielectric material,parasitic capacitance, triboelectric noise, piezoelectric noise, anddielectric absorption, etc.

Accordingly, there is a need for improved semiconductor test equipmentfor electrically probing semiconductor devices at low currents over awide temperature range.

SUMMARY OF THE INVENTION

To solve the above and the other problems, the present inventionprovides a probe needle apparatus and method including a driven guardhaving the same potential as a probe needle for reducing signal noise inlow current measurements. The probe needle apparatus includes a centralconductive probe needle covered with alternating layers of dielectricand conductive materials.

In one embodiment, the probe needle apparatus comprises a centralconductive probe needle surrounded by a high temperature dielectriclayer of material. A conductive layer is deposited around the dielectriclayer to provide a driven guard. The initial layer of dielectricmaterial provides a thin and continuous barrier to prevent theconductive driven guard from contacting electrically to the probeneedle. In one embodiment, a subsequent protective layer is applied overthe driven guard.

In one embodiment of the present invention, the probe needle can be aprobe needle disclosed in U.S. Provisional Patent Application Ser. No.60/392,394, filed Jun. 28, 2002, entitled “SHIELDED PROBE APPARATUS FORPROBING SEMICONDUCTOR WAFER”. Also, in one embodiment, the probe needleis masked at the distal and proximate ends to allow continuity. Themasked probe needle is then coated with a flexible high temperaturedielectric, prior to being coated with a conductive layer, such as gold,for the driven guard. An optional top layer can be applied by a method,such as dipping and spinning, or depositing by other means to protectthe outer conductive layer.

In one embodiment of the probe needle, an initial dielectric layer isapplied by dipping and spinning. After thermally curing the dielectriclayer, the conductive layer for the driven guard is applied.

Additionally in one embodiment of the present invention, the probeneedle may be coated with an initial dielectric layer of SiO2. A thinconductive layer of the driven guard may be strengthened byover-plating.

These and other features of the present invention will become apparentto those skilled in the art from the following detailed description,wherein it is shown and described illustrative embodiments of theinvention, including best modes contemplated for carrying out theinvention. As it will be realized, the invention is capable ofmodifications in various obvious aspects, all without departing from thespirit and scope of the present invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of one embodiment of a shielded probeapparatus in accordance with the principles of the present invention.

FIG. 2 is a masking technique for masking a shielded probe in accordancewith the principles of the present invention.

FIG. 3 is a rotational technique for applying one or more conformalcoatings on the shielded probe in accordance with the principles of thepresent invention.

FIG. 4 is a cross sectional view of another embodiment of a shieldedprobe apparatus in accordance with the principles of the presentinvention.

FIG. 5 is a perspective view of one embodiment of a probe apparatushaving a co-axial shielded probe terminating with a co-axial signalcable at a terminating device, in accordance with the principles of thepresent invention.

FIG. 6 is a perspective view of one embodiment of a probe apparatushaving a tri-axial shielded probe terminating with a tri-axial signalcable at a terminating device, in accordance with the principles of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description of a preferred embodiment, reference ismade to the accompanying drawings, which form a part hereof, and inwhich is shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

For purposes of explanation, numerous specific details are set forth inthe following description in order to provide a thorough understandingof the present invention. However, it will be evident to one of ordinaryskill in the art that the present invention may be practiced withoutsome of these specific details.

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetailed preferred embodiment of the invention with the understandingthat the present disclosure is to be considered as an exemplification ofthe principles of the invention and is not intended to limit the broadaspect of the invention to the embodiment illustrated.

The numerous innovative teachings of the present application will bedescribed with particular reference to the presently preferredembodiments, wherein these innovative teachings are advantageouslyapplied to the particular problems of a probe needle for measuring lowcurrents with a wide operating temperature range in probing asemiconductor device. However, it should be understood that theseembodiments are only examples of the many advantageous uses of theinnovative teachings herein. In general, statements made in thespecification of the present application do not necessarily limit any ofthe various claimed inventions. Moreover, some statements may apply tosome inventive features but not to others. In general, unless otherwiseindicated, singular elements may be in the plural and visa versa with noloss of generality.

The following terms are particularly described throughout thedescription:

Semiconductor Device Not Limitive

The present invention is particularly suitable for probing semiconductordevices, but the use of the present teachings is not limited to probingsemiconductor devices. Other devices may be applied to the presentinvention teachings. Thus, while this specification speaks in terms ofprobing ‘semiconductor’ devices, this term should be interpreted broadlyto include probing any suitable device.

Low Current Not Limitive

The present invention solves the problem of measuring currents below 100fA, but the current range of the present teachings is not limited tobelow 100 fA. For example, the present invention may be applied tomeasure the currents at or above 100 fA in a semiconductor device. Thus,while this specification speaks in terms of ‘low currents’ or ‘measuringcurrents below 100 fA’, these terms should be interpreted broadly toinclude any current that flows through a semiconductor device whichcould be at or above 100 fA. In a grounded guard controlled impedanceconfiguration the present invention also solves the problem of measuringhigh frequency signals at high temperatures.

Wide Temperature Not Limitive

The present invention solves the problem of measuring currents of asemiconductor device in a narrow or limited operating temperature range.The present teachings do not limit to a specific operating temperaturerange. The present application allows a tester to electrically probesemiconductor devices over a wide operating temperature range, not onlyat a low operating temperature but also a high operating temperature,e.g. an operating temperature up to 300° C. and beyond. Thus, while thisspecification speaks in terms of ‘wide temperature range’ or ‘measuringcurrents in a wide operating temperature range’, these terms should beinterpreted broadly to include any suitable operating or testingtemperature range of a semiconductor device.

Probe Not Limitive

The present invention solves the problem of measuring currents of asemiconductor device using a co-axial or a tri-axial shielded probe.However, nothing in the teachings of the present invention limitsapplication of the teachings of the present invention to a probe needlewith more or less layers. Advantageous use of the teachings of thepresent invention may be had with a probe needle of any number oflayers.

Signal Cable Not Limitive

The present invention solves the problem of measuring currents of asemiconductor device using a co-axial or a tri-axial signal cable.However, nothing in the teachings of the present invention limitsapplication of the teachings of the present invention to a signal cablewith more or less layers. Advantageous use of the teachings of thepresent invention may be had with a signal cable of any number oflayers.

Metals Not Limitive

Throughout the discussion herein there will be examples provided thatmake reference to metals in regards to needle and driven guard. Thepresent invention does not recognize any limitations in regards to whattypes of metals may be used in affecting the teachings of the presentinvention. One skilled in the art will recognize that any conductivematerial may be used with no loss of generality in implementing theteachings of the present invention.

Dielectric Not Limitive

Throughout the discussion herein there will be examples provided thatmake reference to dielectric. The present invention does not recognizeany limitations in regards to what types of dielectric may be used inaffecting the teachings of the present invention. One skilled in the artwill recognize that any non-conductive, highly heat-resistant materialmay be used with no loss of generality in implementing the teachings ofthe present invention.

Exemplary Embodiment

As shown in FIG. 1, a shielded probe needle apparatus 100 includes aprobe needle 101 covered with a dielectric layer 102, a conductivedriven guard layer 103, and an optional protective coating layer 104.The dielectric layer 102 and the optional protective coating layer 104are preferably applied to the probe needle 101 using a physical/chemicalvapor deposition (P/CVD) of high temperature polymer.

As also shown in FIG. 1, the connection or contact between the probeneedle 101 side and the connector or signal cable (not shown) side ishead on head. Alternatively, the connection or contact between the probeneedle 101 side and a connector or signal cable 107 side is side-by-sideas shown in FIGS. 5 and 6, which are disclosed in U.S. patentapplication Ser. No. 10/383,079, filed Mar. 6, 2003, subject matter ofwhich are incorporated herewith by reference. FIG. 2 illustrates amasking technique for masking a probe needle 201. As shown, maskingmaterials 202 and 203 are applied to the ends of the probe needle 201 toprevent the conductive driven guard layer 103, such as the conductivedriven guard layer 103 in FIG. 1, from depositing over the end of thedielectric creating a conductive path between the conductive guard layer103 and the probe needle 201. The masks are applied towards the ends ofthe probe needle necessary to provide required access and protection.

Alternate methods may be used to achieve at least similar maskingfunctions to prevent electrical contact between the conductive drivenguard layer 103 and the probe needle 201, and to provide required accessand protection to the probe needle. For example, in one exemplarymethod, the end of the conductive driven guard layer is removed byablation or chemical etch to prevent the conductive driven guard layer,such as the conductive driven guard layer 103 in FIG. 1, from remainingon the dielectric creating a conductive path between the conductiveguard layer and the probe needle 201. The protective coating 104 isapplied over the conductive driven guard layer to provide requiredaccess and protection. The mask is then removed or can be left behind asthe protective layer.

FIG. 3 illustrates a rotational curing technique for coating theshielded probe with dielectric or the conductive guard layer. As shown,a plurality of probe needles 301 are mounted radially on an axiallyrotational rod 304 by devices, such as clamps 302. A layer is uniformlyapplied to the probe needles by dipping or spraying and then spinningthe probe needles. The masks at the ends of the probe needle alsoprevent the protective coating layer from touching the probe needle.Alternatively, the masking is not used and the layer is removed bymechanical or chemical means. Uniformly coated materials can bedeposited and dried by a flow of thermally conditioned and humiditycontrolled gas.

Further, in another alternative technique, a mask is applied one end,e.g. a proximal end (the back end) of the probe needle. After adielectric layer is applied over the probe needle, e.g. a P/CVD layer isdeposited over the probe needle, another mask is applied to the otherend, e.g. a distal end (the tip end) of the probe needle. Next, aconductive layer, such as gold, is sputtered over the dielectric layer.

FIG. 4 illustrates one embodiment of a probe needle apparatus 400 in atri-axial configuration. FIG. 1 illustrates one embodiment of the probeneedle apparatus 100 in a coaxial configuration. As shown in FIG. 4, theprobe apparatus 400 comprises a probe needle 401, a base dielectriclayer 402 covering the probe needle 401, a conductive guard layer 403covering the base dielectric layer 402 which is in turn covered by asecond dielectric layer 404, and a second conductive guard layer or anouter guard layer 405 covering the second dielectric layer 404. Anonconductive protective layer 406 may be added for electrical andmechanical protection.

As briefly discussed above, FIG. 5 shows an embodiment of a probeapparatus having a co-axial shielded probe terminating with a co-axialsignal cable at a terminating device side by side. The followingdetailed descriptions have been disclosed in U.S. patent applicationSer. No. 10/383,079, filed Mar. 6, 2003, subject matter of which areincorporated herewith by reference. In FIG. 5, a probe apparatus 100 aincludes a co-axial shielded probe 108 a terminating with a co-axialsignal cable 102 a at a terminating device 132. The shielded probe 108 aincludes a center conductive probe needle 146 a, a dielectric layer 148a surrounding the center conductive probe needle 146 a, a conductiveguard layer 150 a surrounding the dielectric layer 148 a, anon-conductive heat-shrinkable sleeve 152 a surrounding the conductiveguard layer 150 a. The signal cable 102 a includes a center signalconductor 154 a, a dielectric layer 156 a surrounding the center signalconductor 154 a, a conductive dispersion/guard layer 158 a surroundingthe dielectric layer 156 a, and a non-conductive heat-shrinkable sleeve160 a surrounding the conductive dispersion/guard layer 158 a.

At a distal end 126 a, the shielded probe 108 a extends from thedielectric block 130 toward the bond pad 110. The sleeve 152 a isremoved when it is inserted into the dielectric block 130.

As shown in FIG. 5, at the proximal end 128 a, the center conductiveprobe needle 146 a of the shielded probe 108 a is disposed side by sidewith and electrically connects to the center signal conductor 154 a ofthe signal cable 102 a. The dielectric layer 148 a of the shielded probe108 a is disposed side by side with and connects to the dielectric layer156 a of the signal cable 102 a. The conductive guard layer 150 a of theshielded probe 108 a is disposed side by side with and electricallyconnects to the conductive dispersion/guard layer 158 a of the signalcable 102 a. The sleeve 152 a of the shielded probe 108 a is disposedside by side with and connects to the sleeve 160 a of the signal cable102 a.

As shown in FIG. 5, the terminating device 132 includes a shrink tube162 a for shrink-tubing the sleeve 152 a of the shielded probe 108 a andthe sleeve 160 a of the signal cable 102 a together, for shrink-tubingthe conductive guard layer 150 a of the shielded probe 108 a and theconductive dispersion/guard layer 158 a of the signal cable 102 atogether, for shrink-tubing the dielectric layer 148 a of the shieldedprobe 108 a and the dielectric layer 156 a of the signal cable 102 atogether, and for shrink-tubing the center conductive probe needle 146 aof the shielded probe 108 a and the center signal conductor 154 a of thesignal cable 102 a together. The shrink tube 162 a is covered by thestrain relief 144 a.

An extension 164 a of the shrink tube 162 a is disposed at an end of thecenter conductive probe needle 146 a and the center signal conductor 154a, and is configured sufficiently wide enough to prevent electricalcurrent from leaking from the center conductive probe needle 146 a andthe center signal conductor 154 a to the strain relief 144 a. Inaddition, the center conductive probe needle 146 a and the center signalconductor 154 a may be soldered, brazed, welded, crimped, or snuggledtherebetween at 166 a to provide additional clearance between the centerconductive probe needle 146 a and the strain relief 144 a, andadditional clearance between the center signal conductor 154 a and thestrain relief 144 a.

Similarly, as briefly discussed above, FIG. 6 shows an embodiment of aprobe apparatus 100 b having a tri-axial shielded probe terminating witha tri-axial signal cable at a terminating device side by side. Thefollowing detailed descriptions have been disclosed in U.S. patentapplication Ser. No. 10/383,079, filed Mar. 6, 2003, subject matter ofwhich are incorporated herewith by reference. In FIG. 6, the probeapparatus 100 b includes a tri-axial shielded probe 108 b terminatingwith a tri-axial signal cable 102 b at the terminating device 132. Thetri-axial shielded probe 108 b additionally includes a second dielectriclayer 168 sandwiched between a conductive guard layer 150 b and thesleeve 152 b. A guard layer 169 may be included between the seconddielectric layer 168 and the sleeve 152 b. The signal cable 102 badditionally includes a second dielectric layer 170 sandwiched betweenthe conductive dispersion/guard layer 158 b and the sleeve 160 b. Aguard layer 171 may be included between the second dielectric layer 171and the sleeve 160 b. Accordingly, as shown in FIG. 6, the shieldedprobe 108 b includes a center conductive probe needle 146 b, adielectric layer 148 b surrounding the center conductive probe needle146 b, the conductive guard layer 150 b surrounding the dielectric layer148 b, the second dielectric layer 168 surrounding the conductive guardlayer 150 b, the guard layer 169 surrounding the second dielectric layer168, and the sleeve 152 b surrounding the guard layer 169. The signalcable 102 b includes a center signal conductor 154 b, a dielectric layer156 b surrounding the center signal conductor 154 b, the conductivedispersion/guard layer 158 b surrounding the dielectric layer 156 b, thesecond dielectric layer 170 surrounding the conductive dispersion/guardlayer 158 b, the guard layer 171 surround the second dielectric layer170, and the sleeve 160 b surrounding the guard layer 171.

At a distal end 126 b, the shielded probe 108 b extends from thedielectric block 130 toward the bond pad 110. The sleeve 152 b isremoved when it is inserted into the dielectric block 130.

As shown in FIG. 6, at the proximal end 128 b, the center conductiveprobe needle 146 b of the shielded probe 108 b is disposed side by sidewith and electrically connects to the center signal conductor 154 b ofthe signal cable 102 b. The dielectric layer 148 b of the shielded probe108 b is disposed side by side with and connects to the dielectric layer156 b of the signal cable 102 b. The conductive guard layer 150 b of theshielded probe 108 b is disposed side by side with and electricallyconnects to the conductive dispersion/guard layer 158 b of the signalcable 102 b. The second dielectric layer 168 of the shielded probe 108 bis disposed side by side with and connects to the second dielectriclayer 170 of the signal cable 102 b. The guard layer 169 of the shieldedprobe 108 b is disposed side by side with and electrically connects tothe guard layer 171 of the signal cable 102 b. The sleeve 150 b of theshielded probe 108 b is disposed side by side with and connects to thesleeve 160 b of the signal cable 102 b.

As shown in FIG. 6, the terminating device 132 includes a shrink tube162 b for shrink-tubing the sleeve 152 b of the shielded probe 108 b andthe sleeve 160 b of the signal cable 102 b together, for shrink-tubingthe second dielectric layer 168 of the shielded probe 108 b and thesecond dielectric layer 170 of the signal cable 102 b together, forshrink-tubing the conductive guard layer 150 b of the shielded probe 108b and the conductive dispersion/guard layer 158 b of the signal cable102 b together, for shrink-tubing the guard layer 169 of the shieldedprobe and the guard layer 171 of the signal cable 102 b, forshrink-tubing the dielectric layer 148 b of the shielded probe 108 b andthe dielectric layer 156 b of the signal cable 102 b together, and forshrink-tubing the center conductive probe needle 146 b of the shieldedprobe 108 b and the center signal conductor 154 b of the signal cable102 b together. The shrink tube 162 b is covered by the strain relief144 b.

An extension 164 b of the shrink tube 162 b is disposed at an end of thecenter conductive probe needle 146 b and the center signal conductor 154b, and is configured sufficiently wide enough to prevent electricalcurrent from leaking from the center conductive probe needle 146 b andthe center signal conductor 154 b to the strain relief 144 b. Inaddition, the center conductive probe needle 146 b and the center signalconductor 154 b may be soldered, brazed, welded, crimped, or snuggledtherebetween at 166 b to provide additional clearance between the centerconductive probe needle 146 a and the strain relief 144 b, andadditional clearance between the center signal conductor 154 a and thestrain relief 144 b.

From the above description and drawings, it will be understood by thoseof ordinary skill in the art that the particular embodiments shown anddescribed are for purposes of illustration only and are not intended tolimit the scope of the present invention. Those of ordinary skill in theart will recognize that the present invention may be embodied in otherspecific forms without departing from its spirit or essentialcharacteristics. References to details of particular embodiments are notintended to limit the scope of the invention.

1. A probe needle apparatus having a conductive central core withalternating layers of dielectric and conductive materials, comprising:the conductive central core; a first layer of dielectric materialapplied to maintain electrical access to the conductive central corewhile providing continuous isolation of the conductive central coreelsewhere; and a conductive driven guard layer applied around the firstlayer of dielectric material in electrical isolation from the conductivecentral core; and wherein the conductive driven guard layer is appliedon the first layer of dielectric material with a mask on an end of theconductive central core to prevent the conductive driven guard layerfrom touching the conductive central core.
 2. The apparatus of claim 1,further comprising a protective non-conductive layer applied around theconductive driven guard layer to provide electrical and mechanicalprotection.
 3. The apparatus of claim 2, wherein the first layer ofdielectric material is coated by using a physical/chemical vapordeposition (P/CVD) of high temperature polymer.
 4. The apparatus ofclaim 2, wherein the protective non-conductive layer is applied on theconductive driven guard layer by spinning the conductive central core.5. The apparatus of claim 4, wherein the protective non-conductive layeris applied on the conductive driven guard layer with a mask on the endof the conductive central core to prevent the protective non-conductivelayer from touching the conductive central core.
 6. A probe needleapparatus having a conductive central core with alternating layers ofdielectric and conductive materials, comprising: the conductive centralcore; a first layer of dielectric material applied to maintainelectrical access to the conductive central core while providingcontinuous isolation of the conductive central core elsewhere; and aconductive driven guard layer applied around the first layer ofdielectric material in electrical isolation from the conductive centralcore; wherein the conductive driven guard layer is applied on the firstlayer of dielectric material and removed on an end by mechanical orchemical means to prevent the conductive driven guard layer fromtouching the conductive central core.
 7. The apparatus of claim 6,wherein the protective non-conductive layer is applied on the conductivedriven guard layer by using the chemical vapor deposition (P/CVD) ofhigh temperature polymer.
 8. A probe needle apparatus having aconductive central core with alternating layers of dielectric andconductive materials, comprising: the conductive central core; a firstlayer of dielectric material applied to maintain electrical access tothe conductive central core while providing continuous isolation of theconductive central core elsewhere; a conductive driven guard layerapplied around the first layer of dielectric material in electricalisolation from the conductive central core; a second layer of dielectricmaterial applied to maintain electrical access to the conductive centralcore and the first layer of dielectric material while providingcontinuous isolation of the conductive central core and the conductivedriven guard layer elsewhere; and a second guard layer applied aroundthe second layer of dielectric material; wherein the conductive drivenguard layer is applied on the first layer of dielectric material with amask on an end of the conductive central core to prevent the conductivedriven guard layer from touching the conductive central core.
 9. Theapparatus of claim 8, further comprising a protective non-conductivelayer applied around the second conductive driven guard layer to provideelectrical and mechanical protection.